From German Patent DE 38 29 922 C2, a Bowden tube window regulator is known having a closed cable loop which is guided over guide pulleys mounted at the ends of a guide rail. The adjusting force is produced by a drive unit with a cable drum whose housing has two parallel cable exits. As the cable drum turns, the cable is wound in one direction or the other over the cable drum, and thereby moves the slider which is connected to the cable loop and which on one side is in positive displaceable engagement with the guide rail and on the other is fixed on the window pane.
Separate cable sleeves are fitted on the ends of the parallel cable exits of the cable drum housing. The free ends of the cable sleeves have thickened ends in which the ends of the flexible Bowden tubes are fitted. On the other side, coil springs are supported between the thickened ends and the housing of the cable drum to hold the cable loop under tension. As the cable length increases, the displaceable cable sleeves are pushed somewhat more out of their guide in the cable drum housing which quasi amounts to an extension of the Bowden tube.
However, there is the drawback that the described cable length compensation has a relatively large reverse play since as a result of the change of rotary direction one time the coil spring of one cable exit and one time the coil spring of the other cable exit is compressed more or less depending on strain. This reverse play can indeed be reduced by using stronger springs but with the drawback of ever increasing friction in the Bowden system and the loss of efficiency of the drive system connected therewith. Furthermore the compensating path provided for compensating the cable must be set out in both cable sleeves.
From German Patent DE 27 50 904 A1, a Bowden tube window regulator of the type described above is known where the cable sleeves biased by a tension spring are supported by a lock acting against the tension force. For this, each cable sleeve supports saw tooth like elements in which a spring-like locking element can engage. The locking element prevents the tension spring from becoming compressed when the window regulator is operated (loaded). Thus a reverse play cannot occur. However there is the drawback that the device described also compensates those cable slacks which occur as a result of the tension of the window regulator in the unstressed area of the cable on the other cable exit. A cable slack of this kind corresponds to a non-genuine cable slack (play), and in the event of its compensation after relaxation of the window regulator leads to tensions remaining in the system. The degree of efficiency is thereby impaired and the wear on the adjustment device increases. Furthermore this tension leads to premature further cable extension whereby a particularly large compensation path has to be set out in the device for cable length compensation.
A further variation of this specification provides a displaceable or eccentrically mounted cable guide pulley at the end of the guide rail which with the support of a tension element with the appearance of cable slack is to carry out a corresponding displacement movement. Through a lock with keyed locking elements it is ensured that a resetting movement is ruled out when loading the window regulator. In addition to the disadvantages described above, setting movements of the cable guide pulleys cause a changed angular cable guide which lead in addition to friction and wear.
From European Patent 0 607 589 A1, an infinitely operating device is known for compensating cable extensions. The cable sleeves mounted displaceable in a base member engage with a spring-like clamping element which allows movement of the cable sleeve only in the direction of the tension spring and is supported on the base member.
The drawback with this device is in particular the high surface pressure between the clamping element and cable sleeve which is required for a safe operation, that is for a reliable prevention of a resetting movement of the cable sleeve. However, with the appearance of large forces in connection with high temperatures this can easily lead to damage to the plastic body of the cable sleeve and even to a failure of the compensating device.